High efficacy white LED

• US 20060138937A1
• Filed: 09/15/2005
• Published: 06/29/2006
• Est. Priority Date: 12/28/2004
• Status: Active Grant

• Current Assignee: Creeled Incorporated
• Original Assignee: CREE Incorporated (Wolfspeed, Inc.)
• Inventors: Ibbetson, James
• Granted Patent: US 8,288,942 B2
• Time in Patent Office: Days
• US Class Current: 313/502
• CPC Class Codes: F21K 9/68 Details of reflectors forming part of the light source
• CPC Class Codes: H01L 2224/73265 Layer and wire connectors
• CPC Class Codes: H01L 33/20 with a particular shape, e.g. curved or truncated substrate
• CPC Class Codes: H01L 33/32 containing nitrogen
• CPC Class Codes: H01L 33/507 the elements being in intimate contact with parts other than the semiconductor body or integrated with parts other than the semiconductor body
• CPC Class Codes: H01L 33/54 having a particular shape

Abstract

A white light emitting solid-state lamp is disclosed having an output of at least 75 lumens per watt at 20 milliamps drive current. The lamp includes a light emitting diode, an encapsulant, and a header. The diode includes a conductive silicon carbide substrate for electrical contact and a Group III nitride active portion on the silicon carbide substrate for generating desired frequency photons under the application of current across the diode. The header includes a reflective cup for supporting the diode and for providing electrical contact to the diode and to the active portion. The encapsulant includes a phosphor, present in at least portions of the encapsulant for generating responsive frequencies when the phosphor is excited by the frequencies emitted by the diode.

Claims

1. A white light emitting solid-state lamp comprising:

a light emitting diode, an encapsulant, and a header;

said diode comprising a conductive silicon carbide substrate for electrical contact and

a Group III nitride active portion on said silicon carbide substrate for generating desired frequency photons under the application of current across said diode;

said header comprising a reflective cup for supporting said diode and for providing electrical contact to said diode and to said active portion;

said encapsulant including a phosphor, present in at least portions of said encapsulant for generating responsive frequencies when said phosphor is excited by the frequencies emitted by said diode; and

an output of at least 75 lumens per watt at 20 milliamps drive current.

2. A solid state lamp according to claim 1 with an output of at least 80 lumens per watt at 20 milliamps drive current.

3. A solid state lamp according to claim 1 with an output of at least 85 lumens per watt at 20 milliamps Drive current.

4. A solid state lamp according to claim 1 comprising a conductive silicon carbide substrate having a single polytype;

at least one p-type Group III nitride layer on said substrate; and

at least one n-type Group III nitride layer on said substrate in a vertical orientation.

5. A solid state lamp according to claim 1 comprising an ohmic contact to one of said Group III nitride layers with said ohmic contact being in physical and electrical contact with said header.

6. A solid state lamp according to claim 1 wherein said reflective cup includes a silver coating for maximizing light extraction from said lamp.

7. A solid state lamp according to claim 1 wherein said encapsulant comprises an epoxy resin.

8. A solid state lamp according to claim 1 wherein said phosphor emits responsive frequencies in the yellow portion of the visible spectrum when excited by frequencies emitted from the group consisting of the ultraviolet, violet and blue portions of the electromagnetic spectrum.

9. A solid-state lamp according to claim 8 wherein said phosphor comprises cesium yttrium aluminum garnet.

10. A solid state lamp according to claim 1 wherein said diode emits photons having frequencies selected from the group consisting of the ultraviolet, violet and blue portions of the electromagnetic spectrum.

11. A solid state lamp according to claim 1 comprising at least one p-type Group III nitride layer and an ohmic contact to said p-type layer, said ohmic contact having an average thickness of between about 1 and 250 Å

.

12. A solid state lamp according to claim 11 wherein said ohmic contact has an average thickness of between about 1 and 10 Å

.

13. A solid state lamp according to claim 1 wherein said diode has a total dimension between and including any ohmic contacts of no more than 250μ

.

14. A solid state lamp according to claim 1 wherein said diode has a total dimension between and including any ohmic contacts of no more than 100μ

.

15. A white light emitting diode-based lamp comprising:

a light emitting diode that emits in a portion of the spectrum selected from the ultraviolet, blue, and violet portions of the electromagnetic spectrum;

a dimpled header supporting said diode, said dimple having a (functional) shape that maximizes the extraction of light from the diode in said dimple;

a first portion of encapsulating resin covering said diode in said dimple and filling said dimple only to the extent necessary to cover said diode;

a second portion formed of a mixture of said encapsulating resin with a phosphor and filling the remainder of said dimple to thereby separate said phosphor containing portion sufficiently from said diode to minimize said diode'"'"'s absorption of light from the phosphor that can otherwise be extracted; and

a lens on said filled dimple formed of said encapsulating resin for increasing and maximizing the extraction of light from the lamp.

16. A diode-based lamp according to claim 15 comprising an ohmic contact to a p-type Group III nitride layer that has an average thickness of between about 1 and 250 Å

.

17. A diode-based lamp according to claim 16 wherein said ohmic contact has an average thickness of between about 1 and 10 Å

.

18. A diode-based lamp according to claim 15 wherein said diode has a total dimension between and including any ohmic contacts of no more than 250μ

.

19. A diode-based lamp according to claim 15 wherein said diode has a total dimension between and including any ohmic contacts of no more than 100μ

.

20. A diode-based lamp according to claim 15 wherein said light emitting diode comprises at least a conductive silicon carbide substrate and a Group III nitride active portion.

21. diode-based lamp according to claim 20 wherein said diode comprises a single crystal silicon carbide substrate, at least one p-type Group III nitride layer and at least one n-type Group III nitride layer in a vertical orientation.

22. A diode-based lamp according to claim 20 wherein said diode is positioned on said header in a flip chip orientation.

23. A diode-based lamp according to claim 15 wherein said diode emits in a portion of the spectrum selected from the ultraviolet, violet, and blue portions of the electromagnetic spectrum.

24. diode-based lamp according to claim 15 wherein said dimpled header is plated with a reflective metal (conductive).

25. A diode-based lamp according to claim 24 wherein said metal comprises silver.

26. A lamp according to claim 15 wherein said first portion of encapsulating resin, said second portion of encapsulating resin, and said lens are all formed of an epoxy resin.

27. A diode-based lamp according to claim 15 wherein said phosphor emits light in the yellow portion of the visible spectrum in response to the light emitted by said diode.

28. A diode-based lamp according to claim 27 wherein said phosphor comprises cesium yttrium aluminum garnet.

29. A diode-based lamp according to claim 15 comprising a slug-type package.

30. A diode-based lamp according to claim 15 comprising a cup-type package.

31. A packaged light emitting diode lamp comprising:

a conductive header;

a light emitting diode on said header, said diode comprising a silicon carbide substrate, at least one active layer of indium gallium nitride, ohmic contacts in a vertical orientation with respect to said substrate and said active layer, and with the ohmic contact to the active layer being in electrical contact with said header;

an encapsulant covering said diode and at least portions of said header;

a phosphor in said encapsulant that emits visible light in response to the emission from said diode; and

said packaged diode demonstrating at least 57 lumen per watt of white light at an operating current of 350 milliamps.

32. A packaged light emitting diode lamp comprising:

a conductive header;

a light emitting diode on said header, said diode comprising a silicon carbide substrate, at least one active layer of indium gallium nitride, ohmic contacts in a vertical orientation with respect to said substrate and said active layer, and with the ohmic contact to the active layer being in electrical contact with said header;

an encapsulant covering said diode and at least portions of said header;

a phosphor in said encapsulant that emits visible light in response to the emission from said diode; and

said chip demonstrating at least 142 lumens per watt of white light at an operating current of 1 amp.

33. A method of forming a high efficiency white emitting semiconductor-based lamp, the method comprising:

forming a cup-shaped dimple into a header base for providing electrical contact and a reflective background and structure;

positioning a high frequency light emitting diode in the dimple and in electrical contact with said header;

partially filling the dimple cup with an encapsulation material in an amount sufficient to cover the diode without filling the cup;

curing the partially filled encapsulation material;

filling the remainder of the dimple cup with a mixture of the encapsulation material and a phosphor responsive to the frequency produced by the diode to thereby separate the phosphor from direct contact with the diode to thereby minimize the diode'"'"'s absorption of phosphorescent light;

curing the remaining encapsulation material in the dimple cup;

forming a solid lens of encapsulation material on the cured material in the dimple cup to enhance the extraction of light from the diode; and

curing the lens material to form the finished lamp.

34. A method according to claim 33 comprising positioning a high frequency light emitting diode in the dimple cup that includes at least a conductive silicon carbide substrate and at least one active portion of a Group III nitride in a vertical orientation.

35. a method according to claim 34 comprising etching the face of the silicon carbide substrate that is opposite to the at least one Group III nitride active portion using an aqueous etch to remove damaged portions of the substrate and thereby increase the light extraction from the resulting diode and the lamp.

36. A method according to claim 33 wherein the step of positioning the diode in the cup-shaped dimple comprises positioning a diode that emits in a portion of the spectrum selected from the blue, violet, and ultraviolet frequencies.

37. A method according to claim 33 wherein the step of filling the dimple cup with an encapsulation material comprises filling the cup with an epoxy resin.

38. A method according to claim 33 wherein the step of filling the dimple cup with an encapsulation material comprises filling the cup with a material having a refractive index greater than 1.0.

39. A method according to claim 33 wherein the step of filling the dimple cup with an encapsulation material comprises filling the cup with a material having a refractive index, greater than 1.5.

40. A method according to claim 33 wherein the step of filling the remainder of the dimple cup with the mixture of encapsulation material and the phosphor comprises filling the cup with a mixture that includes a phosphor that emits in the yellow portion of the visible spectrum in response to light having a frequency selected from the group consisting of the ultraviolet, violet and blue portions of the spectrum.

41. A method according to claim 40 comprising filling the remainder of the dimple cup with a mixture of the encapsulation material and a cesium yttrium aluminum garnet (Ce:

YAG) phosphor.